The present invention relates to a foldable tailgate for load beds at a mining dumper according the preamble of claim 1. The invention also relates to a load bed with such a foldable tailgate according to the preamble of claim 9. The invention also relates to a vehicle with such a load bed according to the preamble of claim 11.
Foldable tailgates to load beds and cargo vehicles are previously known. Such tailgates are pivotally mounted in two or more points at the load bed and may be automatically foldable. It is also known to arrange downward-going tailgates on load beds. The tailgates often have a hinge welded to the outermost rear edge of the load bed and are opened with a linkage, which is mounted on the tailgate.
There are also tailgates which open upwards as they usually are hinged in the upper edge of the load bed and are controlled in the same way.
In the mining equipment, there is also a combination of these tailgates, namely two part tailgates where one opens upwards and one opens downwards.
One problem with tailgates that open downwards and are hinged in the outermost rear edge of the load bed is that the tailgate decreases the clearance when tilting and since it during tilting is closer to the ground than the trailing edge of the load bed. This mainly applies if the load bed protrudes backwards after the fulcrum of the load bed, causing the rear portion of the load bed to form an overhang. A large overhang is common on mining trucks for underground use. In the event that the tailgate is provided with a linkage at the rear edge of the load bed, the linkage may be damaged at tilting if it comes into contact with the ground or with objects lying on the ground.
The problem with tailgates which open upwards is that an obstruction for the load is formed, since the tailgate and its linkage are arranged transversely across the upside of the load bed. This causes the load to hit parts of the tailgate during tilting, which results in great stress on the tailgate, which thus may break down.
The document U.S. Pat. No. 3,322,464 A shows a truck with a load bed, which is provided with a foldable tailgate. A hydraulic cylinder is arranged to pivot the tailgate between an open and closed position. In the open position, the tailgate protrudes backwards from the load bed.
The document SE391898 B shows a foldable tailgate for a vehicle platform. The tailgate comprises a lower and upper tailgate. An articulated coupling is arranged between the lower tailgate and the platform. A hydraulic cylinder connected to the platform and the articulated coupling is arranged to pivot the lower tailgate between an open and closed position. In the open position, the lower tailgate is projecting backwards from the platform and forms an enlargement of the platform surface.
In order to empty a load bed of, for example, a mining dumper, the load bed is provided with a controlled tailgate arranged to be moved between a closed and an open position. The load bed may be either tiltably or fixedly arranged at the mining dumper. When the load bed is fixedly arranged at the mining dumper an ejector gate located at the front end of the load bed is arranged to push the load of the load bed, when the controlled tailgate is in its open position. A common denomination for such a load bed is ejector bed.
Especially at a type of mining dumper, which is provided with a fixed load bed and which is utilized when unloading in areas with low height, where a tilting load bed is not possible to use, the controlled tailgate moves downwards towards the rear wheels, when the same is opened for unloading the contents.
When opening the controlled tailgate at a mining dumper with a fixed load bed of the above mentioned type, a problem arises in that the available movement distance at opening of the controlled tailgate is limited, that is, the height from the ground to the bottom of the load bed is limited. This means that the load which may be loaded onto the load bed will be limited by the height of the controlled tailgate.
The sides of the load bed are usually higher than the height of the controlled tailgate in its closed position. The rear portion of the sides of the load bed therefore usually slopes obliquely backwards towards the upper edge of the controlled tailgate, wherein a dead space occurs where no load can be placed.
One way to reduce this problem is to configure the controlled tailgate in the form of a circular arc and allowing a part of the lower portion of the arc-shaped, controlled tailgate to move in between the rear pair of wheels of the mining dumper with fixed load bed. This way, the height of the controlled tailgate may be increased and the load capacity of the load bed may thus be increased. The height of the tailgate will however remain lower than the sides of the load bed. The tailgate is opened and closed by means of hydraulic cylinders arranged on both outer sides of the load bed, which are both connected to the sides of the load bed and to the tailgate. The location of the hydraulic cylinders on the outer sides of the load bed does however mean that they may be subjected to stress and break down if the load bed is, for example, used in a mine adit and the cylinders ram into the walls of the adit.
The document SE530295 B shows a mechanical tailgate for load beds where the opening and closing movement of the tailgate is in the form of a circular movement. In the open position the tailgate is located under the load bed. The opening and closing of the tailgate is achieved by means of hydraulic cylinders arranged on both sides of the load bed. The load bed is provided with a push plate, which pushes the load out of the load bed.